Hydrocarbons may be recovered from hydrocarbon-bearing formations by penetrating the formation with one or more wells. Hydrocarbons may flow to the surface through the wells. Conditions (e.g. permeability, hydrocarbon concentration, porosity, temperature, pressure, amongst others) of the hydrocarbon containing formation may affect the economic viability of hydrocarbon production from the hydrocarbon containing formation. A hydrocarbon-bearing formation may have natural energy (e.g. gas, water) to aid in mobilizing hydrocarbons to the surface of the hydrocarbon containing formation.
Natural energy may be in the form of water. Water may exert pressure to mobilize hydrocarbons to one or more production wells. Gas may be present in the hydrocarbon-bearing formation (reservoir) at sufficient pressures to mobilize hydrocarbons to one or more production wells. The natural energy source may become depleted over time. Supplemental recovery processes may be used to continue recovery of hydrocarbons from the hydrocarbon containing formation. Examples of supplemental processes include waterflooding, polymer flooding, alkali flooding, thermal processes, solution flooding or combinations thereof.
In chemical enhanced oil recovery (cEOR) the mobilization of residual oil saturation is achieved through surfactants which generate a sufficiently (ultra) low crude oil/water interfacial tension (IFT) to give a capillary number large enough to overcome capillary forces and allow the oil to flow (I. Chatzis and N. R. Morrows, “Correlation of capillary number relationship for sandstone”. SPE Journal, Vol. 29, pp 555-562, (1989).
Compositions and methods for enhanced hydrocarbons recovery utilizing an alpha olefin sulfate-containing surfactant component are known. U.S. Pat. Nos. 4,488,976 and 4,537,253 describe enhanced oil or recovery compositions containing such a component. Compositions and methods for enhanced hydrocarbons recovery utilizing internal olefin sulfonates are also known. Such a surfactant composition is described in U.S. Pat. No. 4,597,879.
U.S. Pat. No. 4,979,564 describes the use of internal olefin sulfonates in a method for enhanced oil recovery using low tension viscous water flooding. An example of a commercially available material described as being useful was ENORDET IOS 1720, a product of Shell Oil Company identified as a sulfonated C17-20 internal olefin sodium salt. This material has a low degree of branching. U.S. Pat. No. 5,068,043 describes a petroleum acid soap-containing surfactant system for waterflooding wherein a cosurfactant comprising a C17-20 or a C20-24 internal olefin sulfonate was used. In “Field Test of Cosurfactant-enhanced Alkaline Flooding” by Falls et al., Society of Petroleum Engineers Reservoir Engineering, 1994, the authors describe the use of internal olefin sulfonates in a waterflooding composition.
In WO2011100301 the use of internal olefin sulfonates is described in conjunction with viscosity reducing compounds. Similarly, Barnes, et al. (SPE-129766-PP “Application of Internal Olefin Sulfonates and Other Surfactants to EOR. Part 1: Structure—Performance Relationships for Selection at Different Reservoir Conditions”, SPE Improved Oil Recovery Symposium, Tulsa, Okla., USA, 24-28 Apr. 2010) reported on the use of internal olefin sulfonate (IOS), in particular IOS 19-23 and IOS 20-24, based surfactant systems for chemical enhanced oil recovery applications. According to Barnes et al., given the potentially large volumes of surfactants that need to be manufactured and transported to the field, it is highly desirable that the surfactant active matter, i.e. the internal olefin sulfonates, be at as high concentration as possible in order to reduce transportation costs and logistical issues.
The internal olefin sulfonates may be provided in concentrated form containing typically 15 wt % or more of internal olefin sulfonates (also referred to as active matter). However, the fluids that are injected into the reservoir comprise relatively low concentrations of the internal olefin sulfonates. These fluids that are injected are prepared by diluting small amounts of the concentrated internal olefin sulfonate with water or brine and optionally other compounds. In order to tailor the enhanced oil recovery conditions for each reservoir it is important to provide an injectable fluid having a uniform composition. Consequently, the concentrated internal olefin composition used to prepare the injectable fluid is required to have a uniform composition.
Due to the nature of the composition, which comprises water as well as components with varied hydrophobic strength such as relatively more hydrophilic hydroxy sulfonates and relatively more hydrophobic alkene sulfonates, the concentrated internal olefin composition can be prone to phase separation. Such phase separation is undesired as the separate phases have a different composition, which may lead to variation in the composition of the injectable fluid that is prepared from a concentrated internal olefin composition. The tendency of a batch of internal olefin composition toward phase separation may not always be visibly detected directly following the production of the batch. It is possible that the internal olefin composition phase separates during transport to the oil production site and could be used to prepare injectable fluid having a non-uniform composition. There is a need in the art for internal olefin compositions that have an increased physical stability, i.e. that have a reduced tendency to phase separate prior to the mixing of the internal olefin composition with any other components, such as water or brine, to form the injectable fluid.